Experimental study of sheath dynamics after current zero of AMF-stabilized vacuum arc

Langmuir-probe-based diagnostics of sheath dynamics in the conditions of current zero followed by TRV escalation were performed for both freely burning vacuum arc with CuCr25 electrodes as well as arc stabilized by axial magnetic field of 7 mT/kA. Tests were done using synthetic circuit and experimental set-up simulating vacuum circuit breaker under short-current operation. The sheath boundary in the case of AMF-stabilized arc was found to expand radially/tangentially away from gap axis unlike the case of freely burning arc where the sheath boundary expands rather spherically away from the electrode hot spot. Besides, plasma density at CZ is much lower in the case of AMF-stabilized arc.